In the architecture of a system architecture evolution (SAE) communications system, a terminal accesses a mobility management entity (MME) and a serving gateway (S-GW) of a core network through an evolved NodeB (eNodeB or eNB), and is connected to a packet data network gateway (P-GW) through the S-GW.
Small data transmission is a special type of data transmission in a wireless communications network system. User plane bearers (including a core network side and an air interface side) need to be established by using signaling to perform data transmission; however, small data (usually less than 1 Kbyte) may be transmitted infrequently, for example, only transmitted once or twice; and in this case, a user plane is established for the small data transmission by using signaling to transmit the data, and after the transmission is completed, an air interface bearer needs to be deleted, which wastes a signaling resource.